ICs (integrated circuits) with predominant digital functionality mostly include a separate power supply terminal for each voltage domain. If, for example, the IC includes a digital controller, which operates at 1.5V, and further input terminals and output terminals configured to receive and output 3.3V signals, then the IC includes at least one power supply terminal for applying 1.5V (or a plurality of internally interconnected power supply terminals may be provided) and at least one further power supply terminal for applying 3.3V. The supply voltages are provided by external voltage regulators. Furthermore, the supply voltages may need to be buffered by capacitors which are coupled in parallel to the supply terminals. The buffering is required since the time scale on which the power consumption of the predominantly digital IC changes is orders of magnitude shorter than the time scale on which the external voltage regulator would be able to react to sudden step-like load variations and adjust the supply voltage which is provided to the load, for example represented by the IC. The power consumption of predominantly digital ICs features pulses the widths of which are on the order of 10 nanoseconds with technologies at 5V (that is, in predominantly digital ICs operating at 5V) and reaching down to 100 picoseconds with technologies at 1.5V (that is, in predominantly digital ICs operating at 1.5V). The pulse-shaped power consumption in (predominantly) digital IC is caused by their synchronous operation. However, control settling times of typical voltage regulators are on the order of approximately 1 microsecond such that they are clearly unable to react to sudden jumps in load conditions caused by the (predominantly) digital IC.
In ordinary voltage regulators usually a single transistor of a voltage domain chosen high enough such that it is designed to handle at least the highest input voltage of the voltage regulator is used as a control device. In addition, operational amplifiers may be used as regulating amplifiers or in circuits fulfilling equivalent functions which provide a high static control precision at the cost of relatively high signal delay times due to the use of multiple amplifying stages. Those two reasons may be seen as mainly responsible for the rather long control settling times of ordinary voltage regulators.
Digital circuits with low power consumption, for example for mobile applications, often include an internal voltage regulator which provides the smaller of the supply voltages such that the other (larger) supply voltage may need to be supplied externally. Those kinds of circuits, however, require the internal low supply voltages to be buffered by external capacitors. Thus, the internal feed lines have to be led to the external of the IC via additional pins, entailing all the disadvantages such as, for example, a required ESD (electrostatic discharge) protection and the necessity to provide additional pins in an integrated circuit.
In digital circuits with even lower power consumption buffer capacitors may be included internally. Examples for such architectures may be found in chip cards or RFID (radio-frequency identification) applications. In addition, circuits in those fields of application are usually not operated in synchronous operation modes in order to reduce the magnitude of the spikes in their power consumption spectrum.
With the trend towards further digitalization, more and more applications are transformed from formerly predominant analog operation mode to digital operation using complex digital circuits. In contrast to digital circuits, the power consumption in analog circuits is largely continuous. Internal low voltage domains and higher supply voltages supplied externally may be easily regulated in analog circuits by means of internal voltage regulators such that they do not have to be led to the external of the IC in order to be buffered, as described in the case of digital ICs. The user of such an analog circuit remains unaware of the internal power supply domains and is uninvolved in their operation. Digital parts of the circuit in such products/applications are mostly operated in asynchronous mode and therefore have a rather small power consumption such that they can be easily supplied with power by internal voltage regulators.
One prominent example of such applications is the field of integrated control circuits for SMPS (switched-mode power supply) which may require a relatively high external supply voltage in the range of 15V to 20V due to the high output voltage of the gate drivers. Such integrated control circuits for SMPS ordinarily maintain an internal voltage domain of 5V in order to supply analog circuit components/parts and, to some extent, digital circuit components/parts with power. The rather complex full digitalization of those applications failed so far mainly due to the requirement of buffering the internal voltage domain for the complex digital (synchronous) logic. As described above, this needs to be done externally by leading out the corresponding feed lines to the external of the IC. Besides the obvious disadvantages that at least one terminal of the IC would be occupied and therefore cannot be used for other purposes/functions, that possibly a bigger housing would have to be used and that the user is rather reluctant to deal with the additional effort involved in providing the buffering functionality, the circuit would be rendered very susceptible to EMI (electromagnetic interference), especially at low internal supply voltages of 1.5V, for example. The vulnerability to disturbances induced by EMI is caused by other surrounding external electrical lines and/or pins carrying substantially higher voltages, for example the drain voltage of the SMPS switching transistors which is usually on the order of 600V or the power mains of the SMPS onto which electrical pulses with magnitudes on the order of 4 kV are applied during EMC (electromagnetic compatibility) testing. For those reasons, the necessity of having to lead out the internal power supply electrical lines to the external of the IC (or its housing) should be avoided.
Up to now the complexity of control circuits for power electronics has been limited to a few hundreds of logic elements which may be implemented in the 5V or the 3.3V voltage domain. Those control circuits are mostly implemented using BiCMOS (bipolar complementary metal-oxide semiconductor) technology which may be used in order to provide BJTs (bipolar junction transistors) which have a gain-bandwidth product which is substantially larger than the gain-bandwidth product of the other components within the digital IC such that the load regulation on the internal power supply line supplying the internal logic in the IC may be limited to a few hundreds of millivolts. However, with the density level of digital ICs constantly rising, the supply voltage of the internal logic continues to decrease together with its accepted absolute tolerance with regard to fluctuations. At the same time, when using those technologies just described for the manufacture of ICs the implementation of the fast BJTs may be too expensive.
More complex digital control circuits (or driving circuits), for example as used in DC-DC converters, are usually subdivided into a digital controller operating with a low supply voltage and one or more separate driving circuits operating with a higher supply voltage which only contain logic arrangements of lower complexity. Control circuits for DC-DC converters typically include a multitude of terminals such that the provision of further terminals for external buffering of the internal logic supply voltage is rather unproblematic.